The invention applies more particularly to systems for “hands-free” access to automotive vehicles. A system for access, referred to as “hands-free” access, to an automotive vehicle allows an authorized user to lock and/or unlock the openings of his or her vehicle without using a key. For this, the vehicle identifies a badge or remote control carried by the user and if the badge or remote control is identified as belonging to the vehicle, then the vehicle locks or unlocks its openings.
This “hands-free” access system is known to a person skilled in the art. It is generally composed of an electronic control unit on board the vehicle, one or more radiofrequency (RF) antennas located on the vehicle and an identification badge or remote control comprising an RF antenna carried by the user.
An identifier exchange between the badge and the vehicle via RF antennas allows the badge to be identified by the vehicle and locking or unlocking to be triggered by the latter.
The identifier may be contained within a portable device other than a badge or a remote control, e.g. it may be contained within a cell phone or a watch worn by the user.
The identifier exchange is generally carried out via radiofrequency (RF) waves and by low frequency (LF) waves. The vehicle first transmits, via the LF antennas, an LF interrogation signal and the badge, if it is located within the reception area of said signal, sends an RF presence message containing its identifier back to the vehicle.
The precise location of the badge around the vehicle is carried out by measuring the intensity of the LF signal, originating from the vehicle, received by the badge (via the antennas and the electronic control unit), which measurements are more commonly known as RSSI (“received signal strength indication” measurements, or measuring the power of a signal received by an antenna on reception). The measurement of the power of the signal, originating from each LF antenna, received by the badge is analyzed by a locating device on board the vehicle, which thereby determines the position of the badge with respect to said LF antennas, i.e. with respect to the vehicle.